It is known that in the polymerization of olefins, especially propylene, any of the a tactic polypropylene, isotactic polypropylene and syndiotactic polypropylene can be produced by choosing a ligand of a metallocene complex among uniform catalysts (a metallocene complex/aluminoxane) for polymerization of olefins (Makromol. Chem. Rapid. Commun. 1983, 4, 417-421; Angew. Chem., Int. Engl. 1985, 24, 507-508; J. Am. Chem. Soc. 1988, 110, 6255-6256; etc.)
Depending on the positions of substituents at the time of synthesis, metallocene complexes may permit the existence of stereoisomers. In the event a mixture of complex isomers formed on synthesis is straightforwardly used for polymerization of olefins where different olefin polymers are produced according to the different nature of the isomers, the resultant polymer will become a mixture of two different polymers. In case a uniform polymer is to be produced, therefore, the mixture of polymers has to be separated. Especially, a C.sub.2 symmetrical crosslinking type metallocene complex tends to form a racemic form and a meso form of isomers in a ratio of 1:1 on its synthesis. On polymerization of propylene, the use of the racemic form permits the production of isotactic polypropylene while the use of the meso form permits the production of atactic polypropylene. Hence, the meso form has to be eliminated in case of producing isotactic polypropylene alone. Separation of the recemic form and the meso form is usually carried out by extraction with a solvent and recrystallization. For obtaining a highly pure racemic form, however, repeating of the separation operations was necessary so that efficiency of the production was extremely low.
In Japanese Laid-open Patent Appln. No.Hei. 10-67793, there is disclosed that a method of changing the racemic/meso ratio wherein unnecessary isomer is decomposed with a decomposing agent such as acidic hydrogen atom or a reactive halogen atom. This method pertains to changing of the racemic/meso ratio by decomposing either one of the isomers, and more precisely, the racemic form is decomposed with ethylene-bis(4,7-dimethylindenyl)zirconium dichloride to obtain the pure meso form.
A number of references are known concerning the reaction for converting a metallocene complex into a .mu.-oxo-complex, for example, Inorganic Chemistry 15, No. 9, 1976 disclosing that dimethylhafnocene is brought into contact with water in the air to form .mu.-oxo-bis(methylhafnocene) and Comprehensive Organometallic Chemistry 3, 1982, 572-576 disclosing that a metaflocene dihalide is converted into a .mu.-oxo-complex in the presence of water and a base.